This invention relates to a method for forming hollow plastic articles and, in particular, to the formation of hollow prosthetic devices.
It is often desirable to form prostheses which replicate the appearance or function of a structure of the human body. Prostheses which are or which contain hollow structures are often desirable for various reasons. A hollow structure is inherently more light weight than an equivalent solid structure. Furthermore, a hollow structure may more nearly replicate the form and function of the body part it replaces.
Various methods of forming hollow plastic prostheses are known in the art. For example, U.S. Pat. No. 5,133,753 issued on Jul. 28, 1992 to Bark, et al. for "Method for Expanding a Self-Sealing Tissue Prosthesis" discloses a self-sealing tissue expander comprising inner and outer layers of relatively non-flowable material and a median layer of flowable material. The shell is expanded by an infusion needle and the self-sealing shell seals an opening in the shell wall following removal of the needle.
U.S. Pat. No. 5,091,121 issued on Feb. 25, 1992 to Nakada, et al. for "Production of a Balloon for an Intraocular Lens" discloses a method of forming a balloon for an intraocular lens by injecting a quantity of adhesive monomer in a mold and polymerizing the monomer while rotating the closed mold about an axis through the centers of the balloon halves. A more typical method of making hollow prostheses is disclosed in U.S. Pat. No. 4,661,187 issued on Apr. 28, 1987 to Beasley for "Method of Making Life-Like Prosthetic Devices." Beasley discloses a method for making prosthetic devices by forming a seamless, flexible, negative mold of a biological body member, casting a positive wax model from the mold, modifying the wax model by sculpturing to the requirements of the individual for whom the prosthesis is being developed, and from the master wax model producing a negative metal mold by electroplating. A curable liquid elastomeric material is then injected into the metal mold to form the outermost layer of the prosthetic device. Rotation of the metal mold is used to evenly disburse the elastomeric material within the mold. In like manner, various additional layers can be formed and pigments and coloring materials added to some of the layers.
In many prostheses it is desirable that a completely enclosed and sealed hollow structure be created. The hollow structure should be capable of maintaining liquid or air in its interior without communication to the exterior. This feature is particularly desirable in order to provide for hollow prosthetic structures which, while maintaining flexibility, tend to return to their original shapes once pressure or stress has been removed. In many applications it is also important that the prosthesis be formed without seams and which fits precisely into the appropriate position on the patient's body.
It is thus desirable to provide for a method of making hollow prostheses which are precise replicates of the human body part being replaced and which further comprise, at least in part, hollow sealed structures which are capable of retaining air or fluid therein.